Let's have a Pulseaudio sink where to feed the input audio for the encoder.
pacmd load-module module-null-sink sink_name=to_radio
sudo apt install cmake
git clone https://github.com/myriadrf/gr-limesdr
cd gr-limesdr
mkdir build
cd build
cmake ..
make
sudo make install
Dream is a free software DRM encoder. The code quality varies but it is usable.
Get the sources:
git svn clone svn://svn.code.sf.net/p/drm/code/dream
Compiling Dream without GUI for tx use to ease running it from a
systemd service. To do that, replace CONFIG at the beginning of file
dream.pro with the following:
CONFIG += warn_on qtconsole
Then run:
qmake
make
If you want to have the graphical user interface as well you can now
rename the binary as dream-console and then rebuild the project with
default config.
Setup Dream.ini:
[Transmitter]
currenttime=CT_OFF
hqiq=0
ifamp=1
ifformat=OF_IQ_POS
iffreq=-4510.0000000
interleaver=SI_LONG
msc=CS_3_SM
protlevel=1
robustness=RM_ROBUSTNESS_MODE_A
samplerateaud=48000
sampleratesig=48000
sdc=CS_2_SM
snddevin=to_radio.monitor
snddevout=-2
spectocc=SO_4
[Transmitter Service 1]
codec=Opus
description=15
id=0
label=MyStation
language=0
Opus_Application=OA_AUDIO
Opus_Bandwith=OB_FB
Opus_Channels=OC_STEREO
Opus_FEC=0
Opus_Signal=OG_MUSIC
The important part is to have snddevout=-2 as it is a magic number
which enables writing I/Q samples to stdout when used with
ifformat=OF_IQ_POS.
TODO Other options still need investigating, especially high quality IQ mode
TODO setting up limesdr transmitter
First, find your LimeSDR serial number and type by running:
LimeUtil --find
See ./lime_iq_tx.py --help for usage instructions. For sure, you
need to define device type (-d), serial number (-s), band setting
(-b), frequency (-f), and gain (-g).
The following example is for my LimeSDR Mini:
{ sleep 6; chrt --rr 95 ./dream -t; } | ./lime_iq_tx.py -f 144.7M -s 1D3AD649AC230B -g 60
Scaling:
chrt --rr 95 ./dream -t | sox -t raw -r 48k -e signed -b 16 -c 2 - -n stat